I'm inviting the Switch Witch over for Halloween this year, but she won't arrive until after my 6-year-old has gone to bed. Are you familiar with the dear old hag? Like Santa or the Tooth Fairy, the Switch Witch visits children while they sleep and leaves a prize. But in this case the prize makes parents happy too, because she swaps it for that overflowing sack of Halloween candy.

We first tried this ingenious ploy last year, when we realized that a triple dose of trick-or-treating—at school, at our neighborhood's Witches' Walk parade, and from going door to door—meant that Harry was likely to haul his weight in bite-size sweets. The prospect terrified me, both for him (his teeth!) and for me (how would I resist the siren song of mini-Twix?). So during the week leading up to the holiday, my husband and I clued Harry in to the Witch's existence and asked him what toy he might like to trade for his leftover candy. He'd still be able to eat some, of course, especially as he'd spend most of the day scarfing sugar, but the more he chose to trade, the larger his prize would be.

Harry bought it, and bought it big. That night he placed his bag of candy at the foot of his bed, and a few hours later it disappeared, replaced with an oft-requested Lightning McQueen toy. My husband and I enjoyed a modest amount of candy that night (okay, maybe it wasn't exactly modest) and gave the rest to our starving-artist neighbors. Wins all around!

The beauty of the Switch Witch story is that it's not part of the traditional Halloween mythology, so you can adapt it to your family's needs: If you're concerned about your child's weight—or your own—this makes it super easy to remove temptation in one fell swoop. If you'd like to instill the spirit of charity, you can embellish the tale with a redistribution theme. If your child struggles with self-control or responsibility, you can suggest that the Witch gives better prizes to kids who eat just a treat or two at a time.

Ready to try it yourself? Here are some tips to get the ball rolling—er, the broomstick flying:

-- Decide what you want the Switch Witch to achieve, and modify the story to fit. Plant the seed ahead of time; don't wait until your kid's putting on his costume to mention it.-- Prizes don't have to be big, expensive items, especially for the youngest trick-or-treaters. Consider how delighted your kid is to get a toy from the gumball machine at the supermarket! Consider stickers, crayons, shiny pennies, tchotchkes from the dollar store—as long as he'll find it roughly equivalent to the amount of candy traded, you can get away with spending very little.-- If you're on a see-food diet, as I am (you see food, you eat it), have a plan for getting that candy out of the house, PDQ. Give it to the teenagers who trick-or-treat after the little ones have gone to bed. Donate it to a food pantry or a women's shelter. Drop it off at the dentist—many collect candy and send it to the troops overseas. Bring it to work and let your colleagues devour it.

The key to pulling off a Switch Witch is to not do it like Marge Simpson: Don't greet your kids at the door dressed like a witch, gleefully snatching all their candy and replacing it with "plain brown toothbrushes, unflavored dental floss, and fun-size mouthwashes." This isn't about taking all the fun out of Halloween. On the contrary, it's about helping kids to understand that fun doesn't have to mean food.